In the prior art, porous, internal, water separators used within a fuel cell are constructed of fine sintered metal structures or graphite structures or tight weave metal structures. One problem common to all of these types of structure is that they have a small bubble pressure which makes the control of the fuel cell difficult and unreliable. Other problems with the prior art porous, internal, water separators is that the all metal porous structures are also heavy, and the porous carbon structures have thin cross sections and are very brittle.
There is a need for a thin, lightweight, hydrophilic water separator that can be used to wick the water produced on the surface of a fuel cell electrode. The water separator must have a high bubble pressure to prevent fuel cell reactants from penetrating through the water separator. The water separator must transmit water through the water separator easily so that water does not build up on the surface of the fuel cell electrode. The water separator must also conduct electricity to the fuel cell.
There is also a need for a hydrophobic gas diffusion layer that is not based on carbon paper. The carbon within the carbon paper is susceptible to oxidation by the oxygen diffusing through the gas diffusion layer.
Another problem that existed in the prior art was the need for a thin, lightweight, hydrophilic water separator that can be used within a water vapor fed electrolysis cell to restrain the cell's water supply within a separate water compartment. Water from this compartment diffuses as a vapor to the electrolysis cell electrode surface and then is electrolyzed. The water separator must have a high bubble pressure to prevent electrolysis gas products from penetrating through the water separator. At the same time, the water separator must easily transmit water through the water separator so that the electrolysis cell does not run out of water and dry up. Also, the water separator must conduct electricity to the electrolysis cell. As with the prior art internal water separators used within fuel cells, prior art water separators used with water vapor fed electrolysis cells have used fine sintered metal structures or tight weave metal structures. These type of structures have a small bubble pressure which makes the restraint of the water difficult and unreliable. The all metal structures are also heavy.
There is also a need for a capillary structure that could be used as part of a thin, heat pipe evaporator that could in turn be used to passively cool electrochemical cells. The capillary structure must have a high bubble pressure to prevent evaporated vapor from penetrating through the capillary structure. The capillary structure must be electrically conductive to conduct electricity from one fuel cell to the next fuel cell in the cell stack. Heat pipe evaporators are not thought to have been previously used to cool electrochemical cells.
In the past, heat pipes typically use a fine sintered structure. But in order to get a sufficiently high bubble pressure, the sintered structure is so dense that it severely restricts the flow of liquid through the sintered material. This reduces the evaporator's effectiveness and its reliability.